The present invention relates to metallic complexes as catalysts for the polymerization or oligomerization of olefins such as alpha olefins and, more particularly, to a catalyst composition that is neutral and does not require the use of activators.
The prior art is replete with numerous catalysts and catalyst systems for use in polymerizing olefins such as alpha olefins. Typically, these catalysts or catalyst systems are well-defined molecular transition metal complexes that normally require an activator such as Lewis and Bronsted acid activators, whose primary role is to abstract a ligand from the neutral transition metal. The net result is the formation of cationic complexes as the catalytic active species. When a material such as methylalumoxane is used, activation also requires methylation of the metal center to obtain an active catalyst.
More rarely, neutral complexes have been found to be catalytically active in the polymerization of olefins. In this regard, in addition to Group 3 complexes, square planar alkyl nickel (II) and alkyl palladium (II) complexes constitute an important class of such catalyst systems. With the right set of ligands, these complexes display activities that parallel those of the cationic systems. Currently, it is believed that polymerization using these catalyst systems involves disassociation of one of the ligands followed by coordination of the olefin that then inserts into a metal-carbon bond.
Another set of neutral complexes that display catalytic activity in the polymerization of olefins are chromium alkyl complexes. Pentamethyl cyclopentadienide chromium dialkyl complexes of the type, Cp*CrR2 wherein Cp*=C5(CH3)5, R=CH2Ph or CH2Si(CM3)3 will readily polymerize various olefins. It is important to note that in these systems catalytic properties are only observed with bulky R groups. Presumably, the bulk of the R group prevents the formation of alkyl bridged dimers thereby insuring the existence of a coordinatively unsaturated chromium center. Such catalysts possess two metal alkyl bonds in which the olefin can insert and do not constitute single site catalysts. Preparation of the latter has been achieved by the use of amido ligand tethered to a cyclopentadienyl. These resulting complexes that have been characterized by X-ray analysis feature remarkable activities in the polymerization of various olefins.
In one aspect, the present invention is directed to a composition of matter for the polymerization or oligomerization of alpha olefins, the composition comprising a compound of the general formula:
[CpM(ArF)Y]pxe2x80x83xe2x80x83(V)
wherein
Cp is a substituted or unsubstituted cyclopentadienyl ligand or cyclopentadienyl-type bulky ligand characterized by one or more open, acylic or fused ring systems comprised of atoms selected from Groups 13-16 of the Periodic Table of Elements and wherein the ligands can include a heteroatom;
M is a transition metal selected from Groups 3-9 of the Periodic Table of Elements;
ArF is a fluorinated aryl group;
Y is a hydrocarbyl group that can contain a heteroatom; and
p is 1 or 2.
Another preferred embodiment of the present invention involves the preparation of the catalyst compound having Formula V. The preferred method comprises reacting a first organometallic compound (hereinafter described as Formula I) with a first metal complex (hereinafter described as Formula II) to form a second, neutral metal complex (hereinafter described as Formula III) and reacting the neutral metal complex with a second organometallic compound (hereinafter described as Formula IV) to produce the catalyst compound (Formula V).
In yet another preferred embodiment of the present invention there is provided a process for the polymerization or oligomerization of an alpha olefin wherein at least one alpha olefin having from 2-20 carbon atoms is reacted in a catalytic system comprising the catalyst compound of Formula V in an inert solvent.